IgG (immunoglobulin G) is useful as diagnostic agents and therapeutic agents, and its demand is expected to be increased. In order to use IgG for such applications, it is necessary to develop techniques to purify IgG at a high purity. In general, for the IgG purification, affinity chromatography using Protein A is used. Protein A is a protein isolated from the cell wall of Staphylococcus aureus and binds to IgG. Since Protein A binds IgG from many of mammalian species, and its binding capacity to IgG per unit protein is large, affinity chromatography which uses a carrier on which Protein A is immobilized is used for industrial antibody purification processes. However, since in the affinity chromatography which uses Protein A, an acidic solution having a pH of at most 4 is used for eluting adsorbed IgG, structure of antibody is likely to be denatured, and associated and aggregated. Further, aggregates are formed in a cell culture step, and it is difficult to remove impurities containing such polymeric IgG by the affinity chromatography using Protein A.
In order to solve the above problem, after the purification by the affinity chromatography using Protein A, a combined method of ion-exchange chromatography and hydrophobic interaction chromatography has been usually used. However, since in the conventional ion-exchange chromatography, separation of an IgG monomer from an impurity containing polymeric IgG is insufficient, a yield of IgG is required to be sacrificed, in order to obtain high purity IgG (namely IgG monomer). Further, in the hydrophobic interaction chromatography, there are problems that a recovery rate is low, and long time is required, which lead to high cost.
On the other hand, various separating agents wherein a polyanion is immobilized on a carrier have been proposed. For example, as a low specific density lipoprotein adsorbing material, an adsorbing material having a high molecule polyanion part having a molecular weight of at least 25,000 on its surface has been known (for example, Patent Document 1). Further, as an adsorbing material for immune complexes, an adsorbing material wherein a compound having an anionic functional group is immobilized on a water-insoluble porous carrier has been known (for example, Patent Document 2). However, in these documents, separating and purifying only an IgG monomer from a mixture containing an IgG monomer and polymeric IgG is not disclosed.
Further, as a separation material for biopolymers (macromolecules), a separation material covered with a polymer wherein surfaces of supporting particles having a hydroxyl group are covalent bonded, has been known (for example, Patent Document 3). In Example E of Patent Document 3, immunoglobulin (IgG) in human serum is separated, however, separating and purifying only an IgG monomer at a high purity is not disclosed. Further, with said separation material, it is difficult to control the molecular weight, molecular weight distribution and graft density (surface density of a graft chain) of a graft chain and the molecular weight of a polymer present on a carrier is low, and therefore, it is considered that separation of an IgG monomer from polymeric IgG would be insufficient.
As mentioned above, in order to use IgG widely as diagnostic agents and therapeutic agents, mass production of a high purity IgG monomer at low cost is necessary. However, there are many unsolved problems in conventional techniques, and in order to solve such problems, development of a novel separating agent and a method for purifying an IgG monomer has been desired.    Patent Document 1: JP-A-59-206045 (claim 1)    Patent Document 2: JP-A-1-68272 (claim 1)    Patent Document 3: JP-1-310744 (claim 1, page 9, upper right column, lines 15 to 19, page 12, lower left column, lines 13 to 20)